Ultra-hard materials such as polycrystalline diamond (PCD) materials and PCD elements formed therefrom are well known in the art. Conventional PCD is formed by subjecting diamond grains, in the presence of a suitable solvent catalyst material, to extremely high pressure/high temperature (HPHT) conditions to promote formation of intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure has enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used for forming conventional PCD include solvent metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent metal catalyst material. The solvent catalyst material is present in the microstructure of the PCD material, in interstitial regions that exist between the bonded together diamond grains.
A problem known to exist with such conventional PCD materials is thermal degradation due to differential thermal expansion characteristics that exist between the interstitial solvent catalyst material and the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., causing ruptures to occur in the diamond-to-diamond bonding, and resulting in the formation of cracks and chips in the PCD structure.
Another problem known to exist with conventional PCD materials is also related to the presence of the solvent catalyst material in the interstitial regions and the adherence of the solvent catalyst to the diamond crystals, and is known to cause another form of thermal degradation. Specifically, the solvent catalyst material causes an undesired catalyzed phase transformation to occur in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of such conventional PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in PCD are known in the art. Generally, these attempts have involved modifying the PCD body in such a manner as to provide an improved degree of thermal stability at the wear or cutting surface of the body when compared to the conventional PCD material discussed above. One known attempt at producing a thermally stable PCD body involves removing the solvent catalyst material from a region of or from the entire PCD body.
This method, which is fairly time consuming, produces a diamond body that may be substantially free of the solvent catalyst material, and is therefore promoted as providing a diamond body having improved thermal stability. However, the resulting thermally stable diamond body can be somewhat brittle and not well suited for certain aggressive wear and/or cutting applications due to the absence of the relatively ductile solvent catalyst material, and/or due to the voids now left in the interstitial regions between the bonded together diamond grains or crystals.
Additionally, in the event that the solvent catalyst material is removed from the entire diamond body, such thermally stable diamond body has a coefficient of thermal expansion that is sufficiently different from that of conventional substrate materials (such as WC—Co and the like), and displays poor wetability to such conventional substrate materials to promote attachment thereto, making it difficult to form a desired attachment with such substrate materials to promote attachment with a desired wear and/or cutting device. This oftentimes results in the diamond body having to be attached or mounted directly to the end-use wear or cutting device, which may be time consuming, and/or not promote a desired strength attachment mechanism, and/or not facilitate positioning of the diamond body on the device in a manner to effect to most effective wear and/or cutting operation of the diamond body.
Another approach that has been used to improve the thermal stability of PCD is to remove the solvent catalyst material from a region of the PCD body near a working surface and then replace the removed solvent catalyst material with a diamond material by the process of chemical or plasma vapor deposition (CVD or PVD). Deposition of diamond by CVD or PVD process is one that results in the infiltration of diamond crystals into the voids or pores created from the removal of the solvent metal catalyst, that produces a PCD construction having a high-density diamond surface. Because the surface portion of the PCD construction is formed from diamond and does not include the catalyst solvent material, it is relatively more thermally stable than the surface of a conventional PCD construction. However, because this PCD construction still includes a region of PCD disposed below the diamond surface, it is still susceptible to the thermal degradation mechanisms noted above for conventional PCD.
It is, therefore, desired that an ultra-hard composite construction be developed in a manner that displays improved thermal and/or mechanical properties when compared to conventional PCD constructions and/or past attempts to make PCD constructions relatively more thermally stable. It is also desired that such ultra-hard composite constructions be capable of accommodating attachment with a suitable substrate to facilitate attachment of the resulting construction to an end-use application device by conventional method such as welding or brazing and the like. It is further desired that such ultra-hard composite constructions and compacts formed therefrom display properties of hardness/toughness and impact strength that are comparable or superior to those conventional thermally stable PCD material described above, and PCD compacts formed therefrom.